1. Field of the Invention
The present invention relates to an antenna device capable of being tuned in a wide band of frequency.
2. Description of the Related Art
A conventional antenna device 10 will be described with reference to FIGS. 6 and 7. A thin metallic strip type of spiral conductor 12 is wound around a ferrite magnetic core 14. Connection terminals 16 and 18 are formed at ends of the spiral conductor 12. The spiral conductor 12 is cut to be divided into a plurality of conductor pieces 12′ and the plurality of conductor pieces 12′ is connected to each other by a plurality of capacitive elements 20. As shown in FIG. 7, the antenna device 10 is one in which the capacitive elements 20 are physically distributed in the spiral conductor 12 to constitute a closed loop, and responds to a specific frequency (for example, Japanese Unexamined Patent Application Publication No. 51-83755 (FIGS. 1 and 3)).
However, according to the conventional antenna device, since the conventional antenna device is resonated with a specific frequency, the receiving sensitivity becomes lowered at a frequency other than the specific frequency when being received over a wide band.